This invention relates generally to output buffer circuits and more particularly, it relates to a composite bipolar/CMOS output buffer circuit having high current drive capabilities and low propagation delay which is compatible with TTL levels.
Conventional output buffer circuits employing CMOS transistors are generally well known in the prior art. The major disadvantage with CMOS transistor technology is that they have a low current drive capability which is unsuitable for large capacitive loads. While the CMOS output buffer circuits of the prior art have been modified to use very large output transistors in order to increase the current drive for TTL level compatibility, this has resulted in the problem of causing substantial propagation delay in its output.
It would therefore be desirable to provide a merged bipolar/CMOS output buffer circuit which has the advantages of high current drive capability and low propagation delay. The present invention is achieved by combining the bipolar transistor and CMOS transistor technologies together. As a result, bipolar transistors and CMOS transistors are merged or are arranged in a common semiconductor substrate to form an integrated circuit output buffer device.